This invention relates to a pipe plug apparatus. According to another aspect, the invention relates to a method for plugging a pipe, particularly in the environment of pipe extrusion.
A common system for extruding plastic pipe utilizes a pressure calibrating or sizing sleeve which receives a pipe therethrough after having been extruded from an extrusion die. According to such a technique, a plug is connected to the die by a cable or other suitable connecting means, and positioned within the pipe downstream from the die. Air is then pumped into the pipe between the die and the plug so as to pressurize the interior of the pipe above atmospheric pressure, typically about 5 to 10 p.s.i.g. Thus, the initially soft pipe being extruded from the die is pressed against the interior surface of the pressure sizing sleeve so as to properly size the pipe while in its soft and heated state. In addition, cooling water is typically circulated through the pressure sizing sleeve to assist in cooling the extruded pipe as it passes through the sleeve.
The above-mentioned plug utilized in the pressure system typically comprises at least two annular seal members connected by a suitable means such as a small diameter rod. Such plugs are quite heavy. For example, a plug employed for the extrusion of a 48-inch diameter pipe would normally weigh as much as 700 pounds. Several disadvantages result from the weight of the plug. One such disadvantage is the poor seal provided by the plug. The excessive weight of the plug provides a good seal between the seal members and the interior surface of the pipe at the bottom portions of the seal members, but a very loose seal is consequently obtained at the top portions of the seal members. Additionally, the weight of the plug causes a tremendous amount of drag on the extruded pipe, thus causing excessive wear of the bottom portions of the seal members, among many other problems. Therefore, the service life of such a plug is relatively short, necessitating frequent replacement of the seal members.